Water Bear is as durable as it is ugly.

1. Tardigrades aka Water Bear can survive being heated for a few minutes to 151 °C or being chilled for days at -272.8 °C (almost absolute zero).
2. Radiation— Shown by Raul M. May from the University of Paris, Tardigrades can withstand 5700 grays of x-ray radiation. (Five grays would be fatal to a human).
3. Pressure—They can withstand the extremely low pressure of a vacuum and also very high pressures, many times greater than atmospheric pressure. In theory, they could even survive the vacuum of space, though the possibility of it is slim.

More about Water Bear here.